Results Long Term UV Exposure

Of particular interest to this study, however, is the reaction of the stones after long-term exposure to intense UV light. The treated samples from Madagascar E(IM), E(IM1) and E(IM2) reacted differently to all other samples, excluding unheated ones (See Table No.1). Significant changes in the color were seen in samples heated with the new treatment E(IM), and a shift towards more yellow or orange was observed (as shown in the Table 1). A color change from near colorless to yellow was also observed in untreated sapphires of Sri Lankan origin (Table 1). This unheated group of sapphires is known to contain specific color centers (Lit. 28). In E(IM) gemstones with an orange body color before the UV experiments, the color shift is more difficult to see. The color change towards more yellow or orange could be reversed when exposed to a gas flame for a short time, and within two days when exposed to a 100 watt halogen lamp at slightly elevated temperatures. A set of white sapphires, which did not change color during the E(IM1)- heating process developed a thin layer of yellow color during the long term UV exposure (shown in Fig. 4). This observation was also made of E(IM1) enhanced blue sapphires (Fig. 4) which have been exposed to UV. The blue samples developed orange edges, while the body color of the sapphires remained unchanged. The color induced by UV treatment could be reversed by short application of heat to all the samples.

Scanning Electron Microscope Analysis (SEM)

Sampling of colored sapphires enhanced by the new treatment in Chantaburi included the study of faceted gemstones E(IM1) (Materials group f.). These gemstones were already faceted in briolette and princess-cut style sapphires prior to heat treatment. By sorting the lots after heat treatment, a set of non-sapphire materials were detected (Fig. 8). The colored samples showed a thin film of interference color at the surface, and were indented by craters due to contact with other minerals in the same heating process. These craters were also found indented on the surface of the sapphires (Fig. 14). The materials were identified as consistent with glass-aggregates, zircon and Chrysoberyl (Table 2).

Furthermore, clusters of sapphires, sintered together by a whitish matrix, were detected. Only an extremely small portion of the gemstones showed this phenomena and it was clear that these were accidental circumstances.

In order to analyze the surfaces of these materials, and to search for potential trace elements used in the process, the materials were studied with a Scanning Electron Microscope (Philips XL 30 ESEM) in February 2002 at the University of Basel's Central laboratory for Microscopy (ZMB) by Technician M. Düggelin and D. Mathys. Five samples were selected (including minerals with an interference film (zircon and Chrysoberyl), and sapphire clusters).

Results SEM

Analyses of zircon and Chrysoberyl did not reveal any further information on chemicals present, other than expected from their chemical compositions and attention was placed on the sapphire clusters and thewhite matrix around the sapphire materials. Cracks and intended craters were investigated, and a series of newly formed crystalites were detected in these cracks (Fig. 16-19), mostly composed of Zr-oxide, plus additional element Silicon (Si), Aluminium (Al) , Magnesium (Mg), Calcium (Ca) and Fluorine (F). Beryllium could not be measured with SEM, and no indications for Chromium (Cr), Titanium (Ti), or Iron (Fe), were found on the surfaces of the enhanced gemstones. Most of the detected elements can be explained as originating from decomposed minerals present in the runs (Si and Zirconium (Zr) from zircon, Al from corundum, or Chrysoberyl), yet the source of F is unclear. Melting on the surface of these minerals is very visible, as different craters are present on the surface of the former faceted materials (Fig. 8) and also by the craters produced at the surface of the sapphires (Fig. 14, 15). They were formed when they came into contact with other chemical compositions present in other minerals - of the same shape, cutting style and size - in the heating run. Chrysoberyl is a potential source for Beryllium. Its role in the heat treatment process is a topic of ongoing international research (Internet Ref. 09, 11, 12, 13). The role of the heavy elements (such as Zr) and, on the other hand, the light elements (such as Beryllium) in the heating runs must be further investigated.